Google Request

I haven’t done one of these in ages (partly because I’ve found more interesting things to write about, but mainly because the google searches that bring people to my blog are usually about me and my work instead of ranom one-line comments about other people or what have you), but here you go:

“can i wash a glaze off of a bisqued pot and then reglaze ?”

Yes. Just be sure you do a good job of scrubbing off the first glaze coat, because otherwise the dust left behind will affect how the new layer deposits itself on your pot, and you could end up with weird bare patches after firing. Also, you’ll have to let your now-saturated pot dry out for a day or two before dipping it in the glaze bucket. It’s okay. It’s a pain in the ass, but you work isn’t ruined.

Google Requests

Today’s burning question is “what causes crazing in pottery”.

The answer: clay and glaze, like pretty much the rest of the universe, expand and contract depending on temperature, atmospheric pressure, etc. Not enough that you’d notice it without a microscope[1], but it happens. The thing is, the clay and the glaze are doing it at slightly different rates, and that creates stress. Over time, cracks form in the glaze. A potter can try to minimize crazing, by formulating a glaze that moves at close to the same rate as the clay, but it’s impossible to match the expansion rate exactly.

[1] Unless someone has actually managed to invent a magical mug that grows bigger every time you pour tea into it. I’d totally buy one of those.

Google Requests

Today’s request is… “blue clay stuff that sticks on walls”.

It’s called sticky tack. (And lots of other things, like blu-tack, stick tack, tik tack, or, wikipedia assures me, zorkai or Prestik.) There are several brands, manufacturing the stuff in several colours, including blue, white, pink, and orange.

It is most definitively not made of clay.

Hope that helps.

Google Requests: The Sequel Strikes Back

This week’s google request is “aqua glazes”.

Well, I’m not going to list off a bunch of recipes, because that would make for an awful lot of typing, and I’m doing this on the last few minutes of my lunch break. But I can give you some guidelines, assuming you’re firing oxidation.

1. Pick a base recipe you like, or that looks interesting. Google “sankey glaze database” or “clayart archives” (or just follow the links in the sidebar) for more recipes than you can shake a stirstick at. Or flip through some old pottery magazines; most of them have a glaze recipe section. (If you’re a CCNL member, you have an entire library of them you can access, in person or by mail.)

2. If the glaze is acidic, adding 1-2% copper carbonate should make it some shade of aqua. If not, try 1-3% copper carbonate and a teeeeny pinch of cobalt carbonate… say, 0,1-05%. Don’t overdo the cobalt; it’s strong stuff, and it’s easy to go from aqua to true blue.

There. That’s really all you need to know.

Google Requests, Part Deux

Wow, Tuesday already. I think time goes faster when you’re sick and not able to pay attention to the world.

Anyhoo, this week’s search is… “what happens to clay when it is overfired”.

My answer: NOTHING GOOD. WHY DO YOU EVEN HAVE TO KNOW? WHAT HORRIBLE THINGS ARE YOU PLANNING TO INFLICT ON YOUR POOR HELPLESS LOYAL KILN, YOU MONSTER?!?

The more technical answer: it melts. Most clays are a mix of actual clays (such as kaolin, bentonite, or ball clays) and a few other minerals (feldspars, talc, various grogs, colourants like iron oxide, etc.). Commercial clays are very carefully formulated so that they have an ideal firing temperature. The “maturing” or “vitrifying” temperature is the point at which the clay reaches its optimum strength and compactness. Below this temperature, it will be porous and fragile. Above it, the clay can warp, bloat, collapse, or even turn into a sad, difficult-to-clean puddle on your kiln shelf. Unless you have some sort of project about the agony of creation, or the warped mind of the artist, or just plain disappointment, I recommend you avoid overfiring your clay.